Pleistocene Epoch

The isotopic record is based on the ratio of two oxygen isotopes, oxygen-16 (
16O) and oxygen-18 (
18O), which is determined on calcium carbonate from shells of microfossils that accumulated year by year on the seafloor. The ratio depends on two factors, the temperature and the isotopic composition of the seawater from which the organism secreted its shell. Shells secreted...